Assuming that petrol is octane C8H18 and has density 0.8 g/ml, 1.425 litre of petrol on complete combustion will consume

Mass  of  octane =d×volume =1.425 ×  103 × 0.8 gMoles  of  octane=1425 × 8114 =10  molesC8H18 + 252 O2 →   8CO2+9H2OFrom the equation it can be seenFor 1 mole octane required 252  moles of oxygen.∴    for  10  moles  octane   required  252 × 10=125  moles of oxygen